Numbers Game: Bye Week Blues

What’s up with all the teams that are coming off a bye still acting like they’re on it? Teams coming off the bye are 3-9 so far this year. Should we blame the new CBA rules that state players must “be given a minimum of four consecutive days off”, and “must include Saturday and Sunday”? Whether the CBA is to blame is debatable, but the plummeting post-bye winning percentage is not. This weekend should be revealing as the two best post-bye coaches in the NFL come off their respective bye weeks: Andy Reid (12-0) and Bill Belichick (9-2). If those coaches can’t win after a bye, no one can. We looked back over the last decade and found that this year’s decline is way outside of the norm.

To better understand just how extraordinary this year’s drop-off is, we plotted a standard bell curve using the league-wide winning percentage after bye weeks since 2000. I know, I’m stepping deep into geekdom here. Try to wipe the glaze from your eyes and stay with me. The league-wide winning percentage after a bye is 54.2% over the last decade (2000-2009). The standard deviation from that mean is 6.9%. You can see on the Bell Curve we plotted that the 2011 winning percentage of 25% is over four standard deviations from the mean. That’s a lot. On a standard bell curve, 68% of all results are expected to fall within 1 standard deviation, and 96% of all results are expected to fall within 2 standard deviations – in this case, two standards deviations would be a winning percentage between 41% and 70%.

Admittedly, 10 years and 316 games is not a very large sample size, but that didn’t deter us from having some fun with numbers. At over 4 standard deviations from the mean, this year’s winning percentage is a 1-in-15,000 year event. In other words, you’re more likely to be injured by a chainsaw or win an Academy Award. So what gives? CBA restrictions are one reasonable theory… or maybe it’s just that the league average got off to a slow start, and post-bye wins are about to start piling up. Only 12 teams have played after their bye so far this year, and those teams have a cumulative winning percentage of 39%. So it’s not like the league’s elite are getting drubbed after byes yet. It seems pretty likely that the post-bye winning percentage will improve. The question is, how much? Andy Reid and Bill Belichick hope to get that rebound started by avoiding the bye week blues with wins this Sunday.